The present invention relates to a roller leveler in which a metal web or strips made of steel, stainless steel, aluminum or the like and having an uneveness refined by a large number of work rollers. The present invention particularly relates to a roller leveler and an automatic depression control unit therefor effective to prevent defects in an aluminum supports used for lithographic printing plates (PS plates) due to extraneous substances having entered into the roller leveler.
In generally-applied roller levelers, a large number of work rollers of small diameter alternately pinch the metal web or strips on the top and bottom thereof to convey the web and repeatedly bend it. As a result, the internal stress in the whole metal web is reduced and distributed and the metal web is flattened and straightened.
Heretofore, in a roller leveler, as shown in FIG. 1, upper work rollers 8 and lower work rollers 9 are depressed to plastically deform a metal web S to flatten the web S. In this operation, the amount of adjustment of depression is controlled according to various factors such as the material, thickness and width of the metal web.
When it is necessary to adjust the shape of a number of metal webs continuously, these metal webs are joined together into a series of metal webs manually (by the operator) or automatically by an automatic metal web joining device upstream of the roller leveler in the roller leveler line. In refining or flattening the series of metal webs with the roller type leveler, sometimes the depression applied to one metal web is not suitable for the next one; that is, it is necessary to change the depression separately depending on the metal webs to be flattened. In this case, the leveling line is operated at low speed, and the operator changes the depression after confirming the passage of the junction of the metal web through the roller leveler.
However, the method is deficient in that, after the passage of the junction through the roller leveler, the amount of adjustment of depression is liable to be set to a value unsuitable for the next metal web in sequence, so that the method produces unsatisfactorily flat metal webs, and a low yield. Also, the method suffers from low productivity because of the low speed operation.
Furthermore, in the generally-applied roller leveler, before metal webs are connected to one another upstream of the roller leveler, sometimes the metal webs are cut crosswise to increase the mechanical strength at the junctions of the metal webs. In this case, the metal webs may have burrs or may be bent, or chips formed in cutting the metal webs may stick to the metal webs.
On the other hand, the roller leveler employs metal work rollers having a hard surface. Therefore, if, as was described above, the metal plates have burrs or are bent, or chips formed in cutting the metal webs stick to the work roller, then the surfaces of the work rollers may be damaged. Furthermore, if extraneous substances such as powdered metal or dust, which are brought into the roller leveler on the metal web, or chips, which are created during correction of the unevenness of the metal web cling to the surface of the work roller, the surface of the work roller may be damaged so as to cause a defect in the surface of the metal web. Alternatively, the diameter of the work roller may be made non-uniform to render the linear velocity of the metal web and the circumferential velocity of the work roller unequal to the each other. Typical of such defects are band flaws, scratches, the clinging of the extraneous substance, side edge wrinkles and improper luster. As a result, the quality of the metal web is deteriorated, such defects on the surface of an aluminum web used to manufacture a lithographic printing plate (PS plate), create serious problems from the viewpoint of the quality and yield of the product.
As countermeasures against these problems of the generally-applied roller leveler, there have been developed a device for shot-blasting the work rollers, as disclosed in Japanese Utility Model Application (OPI) No. 9122/86 (the term "OPI" as used herein means "unexamined published application"), Japanese Utility Model Application (OPI) No. 38318/83 and Japanese Utility Model Application (OPI) No. 99022/84, a device for replacing the work rollers, as disclosed in Japanese Utility Model Application (OPI) No. 91620/81, and a wet leveling method in which a washing liquid is supplied in the process of correcting the unevenness of the metal web to reduce the occurrence of defects, as disclosed in Japanese Patent Application (OPI) No. 117157/76.
However, periodically shot-blasting or replacing the work rollers has a drawback in that it greatly decreases the efficiency of the process of correcting the unevenness. Supplying a washing liquid in the process has a drawback in that the washing liquid adversely affects a coating layer provided on the surface of the metal web especially a coating layer provided on an aluminum support for lithographic printing plate (PS plate), deteriorating the quality of the product.